The present invention relates to a reciprocating piston forming the essential part of numerous heat engine, such as an automobile vehicle engine, a compressor, etc.
Heretofore known pistons generally comprise at least one upper bead having a side surface or periphery which is smooth or generally more or less deeply threaded in order to retain oil facilitating the sliding movement of the piston. With these pistons, it is often noted that wear at the level of the first ring, when it is present, (some pistons of compressors do not comprise any ring) increases with the rise in the power per liter of the engine. Consequently despite all the development of modern technique, mass-produced automobile vehicles comprise reliable engines capable of restoring only 15 to 20%of the potential power of the fuel used. In the case of racing cars, the engines allow only a maximum of 35% of the power of the fuel to be recovered. This is due notably to the excessive friction of the piston which corresponds to half the total friction of an engine, this friction alone constituting a very serious barrier against the increase of the yield.
This undesirable excessive friction is due to the negative action of the driving fluids which exert a pressure on the or each ring of the piston, said pressure tending to apply said rings very strong against the inner wall of the cylinder.